The present invention relates to climate or temperature control of the air in a vehicle passenger compartment and particularly relates to control systems having a heat exchanger in the passenger compartment which receives a flow of engine coolant therethrough for tempering blower air discharged into the passenger compartment.
Vehicle passenger compartment temperature control systems of the aforesaid type are known to employ a blower duct or housing having at least an exothermic heat exchanger or heater core therein for heating blower air. If desired, a second endothermic heat exchanger or evaporator has been interposed upstream of the heater core for circulation of refrigerant therethrough for de-humidifying and cooling blower air before passage over the heater core. In these latter types of systems, it has been found that the temperature of the blower air discharging from the duct plenum into the passenger compartment may be controlled entirely by controlling flow of engine coolant through the heater core thereby eliminating the need for modulating flow of the refrigerant to the evaporator. The desirability of controlling the discharge temperature of the plenum air into the passenger compartment when the refrigerant is being circulated through the evaporator without the need for modulating refrigerant flow has been found to greatly simplify temperature control and comfort level in the vehicle passenger compartment. This is particularly true where it is desired to dehumidify the blower airstream by first cooling the air over the evaporator for condensation of moisture thereon and removal of the same from the blower airstream followed by heating the dehumidified stream to a desired temperature.
It has been particularly desired to provide such a system for tempering blower discharge air temperature in a vehicle passenger compartment wherein the modulation of the flow of coolant to the evaporator core is provided automatically in a manner which maintains the temperature of the air discharging from the blower plenum at a constant level irrespective of changes in the blower speed and the speed of the engine driven coolant pump. It has been particularly desirable to provide such an automatic control system wherein the flow of engine coolant to the heater core is controlled by a servomotor actuated valve.
In providing a control system for operating a servomotor actuated coolant valve to control flow to the heater core, it has been found particular difficult to maintain a constant temperature of discharge air over the heater core where the flow of coolant to the valve varies widely in response to the changes of engine speed between idle and maximum engine operating RPM. Accordingly, it has been desired to find a way or means of automatically controlling the flow of coolant to an automotive passenger compartment heater core to maintain the blower plenum discharge air at a constant temperature despite user selected changes in blower speed and wide swings in the rate of flow of coolant to the coolant valve controlling flow to the heater core inlet.